This invention relates to improvements in steering column assemblies.
It is known to provide a collapsible steering column assembly comprising a steering shaft that is supported within a steering column shroud. To prevent significant injury to the driver in the event of a crash the steering column should be able to collapse as an axial load is applied through the steering wheel, for instance in a front impact where an unrestrained driver is thrown onto the steering wheel.
The steering column shaft may collapse through the use of a weakened section of shaft. However, in a typical modern vehicle the steering shaft is able to collapse telescopically with a first part of the shaft sliding over a second part of the shaft. Advantageously, this same telescopic motion may be used to provide for a range of adjustment of the steering column assembly for reach. In that case, the shaft is typically supported within a shroud that is also telescopic and comprises two portions: an upper shroud portion and a lower shroud portion. A locking mechanism fixes the steering shaft at a desired length, and this is arranged typically so that it is overcome in a crash to permit the desired collapse in length.
To allow a torque to be carried across the two parts of the steering shaft, the end portion of one part of the shaft—typically the upper shaft that is nearest the steering wheel—is hollowed and provided with inwardly extending elongate splines around the circumference of the inner surface. These engage corresponding outwardly facing splines on an end of the other part of the shaft. The splines prevent relative rotation of the two parts of the shaft about their common axis whilst allowing the shafts to slide telescopically. A low friction coating may be provided on the splines in the form of an overmolding, which also has the benefit of allowing the dimensions of the splines to be closely controlled. This is important to prevent the two parts of the shaft tilting relative to one another.
The present invention aims to at least partially ameliorate problems associated with free play present between the two parts of the telescopic steering shaft in such a steering column assembly.